Germination,root elongation,and photosynthetic performance of plants exposed to sodium lauryl ether sulfate (SLES): an emerging contaminant

Environmental Science and Pollution Research - The anionic surfactant SLES (sodium lauryl ether sulfate) is an emerging contaminant, being the main component of foaming agents that are increasingly...     

Study of the reuse of treated wastewater on waste container washing vehicles

The wheelie bins for the collection of municipal solid waste (MSW) shall be periodically washed. This operation is usually carried out by specific vehicles which consume about 5000 L of water per day. Wastewater derived from bins washing is usually stored on the same vehicle and then discharged and treated in a municipal WWTP. This paper presents a study performed to evaluate the reuse of the wastewater collected from bins washing after it has been treated in a small plant mounted on the vehicle; the advantage of such a system would be the reduction of both vehicle dimension and water consumption. The main results obtained by coagulation–flocculation tests performed on two wastewater samples are presented. The addition of 2 mL/L of an aqueous solution of aluminum polychloride (18% w/w), about 35 mL/L of an aqueous solution of CaO (4% w/w) and 25 mL/L of an aqueous solution of an anionic polyelectrolyte (1‰ w/w) can significantly reduce turbidity and COD in treated water (to about 99% and 42%, respectively); the concomitant increase of UV transmittance at 254 nm (up to 15%) enables UV disinfection application by a series of two ordinary UV lamps. Much higher UV transmittance values (even higher than 80%) can be obtained by dosing powdered activated carbon, which also results in a greater removal of COD.     

Non-electrostatic surface complexation models for protons and lead(II) sorption onto single minerals and their mixture

Potentiometric titrations and lead sorption tests were conducted using muscovite, clinochlore, hematite, goethite, quartz, and a mixture of these same minerals. Mechanistic models were developed to represent and interpret these data. The aim was isolating the specific contribution of each mineral in proton and lead binding. Acid-base properties of each single mineral as well as their mixture were represented by discrete models, which consider the dissociation of n monoprotic sites (n-site/n-K(H) models). A one-site/one-K(H) model (logK(H1) = 10.69) was chosen for quartz (dissociation of SiOH edge hydroxyl groups). Goethite and hematite (FeOH groups) were represented by the same one-site/one-K(H) model (logK(H1) = 10.35). Three-site/three-K(H) models were used for muscovite (logK(H1) = 4.18; logK(H2) = 6.65; logK(H3) = 9.67) and clinochlore (logK(H1) = 3.84; logK(H2) = 6.57; logK(H3) = 9.71) assuming that SiOH and AlOH of the aluminosilicate matrix dissociate in the acid-neutral pH range while SiOH groups of quartz inclusions dissociate in the basic range. Similarly, the mixture of these minerals was represented by a three-site/three-K(H) model (logK(H1) = 3.39; logK(H2) = 6.72; logK(H3) = 10.82). According to crossed comparisons with single minerals, the first two sites of the mixture were associated with the aluminosilicate matrix (SiOH and AlOH respectively) and the third site with iron oxides (FeOH) and quartz groups. Additivity of proton binding in the mixture was demonstrated by simulating the mixture's titration curve. A unified model for the entire set of titration curves (single minerals and mixture) was also developed introducing a three-peak distribution function for proton affinity constants. Experimental data for lead sorption onto the mixture and individual minerals in 3-5 pH range denoted the competition between protons and metallic ions. The entire set of lead isotherms (individual mineral and mixture data) was represented adequately by a unified model taking into account both monodentate and bidentate complexes with the three active sites (additivity of lead binding). Experimental data of metal distribution in solid and liquid phases were successfully simulated by implementing the protonation and the surface complexation constants into the database of a dedicated software for chemical equilibria.     

Heavy metal ion influence on the photosynthetic growth of Rhodobacter sphaeroides

The potential of purple non-sulphur bacteria for bioremediation was assessed by investigating the ability of Rhodobacter sphaeroides strain R26.1 to grow photosynthetically in heavy metal contaminated environments. Bacterial cultures were carried out in artificially polluted media, enriched with the transition metal ions Hg2+, Cu2+, Fe2+, Ni2+, Co2+, MoO4(2-), and CrO4(2-) in millimolar concentration range. For each investigated ion the effect on growth parameters was evaluated. The analysis of concentration-effect curves revealed a differentiated response, indicating that diverse mechanisms of tolerance and/or resistance are involved. Adaptation or selection procedures were not applied, leading to assess intrinsic abilities of coping with these contaminants. The microorganism proved to be highly tolerant to heavy metal exposure, especially towards Co2+, Fe2+ and MoO4(2-). In addition Ni2+ and Co2+ were found to decrease the cellular content of light harvesting complexes. A characteristic behavior was observed with mercuric ions, which produced a significant increase of the lag-phase.